1. Field of the Invention
The present invention relates to a liquid crystal display (LCD), and more particularly to a method of producing a color filter for a liquid crystal display which can improve the evenness of the color filter surface layer by eliminating the difference in height between black matrices and color patterns using electroplating.
2. Description of the Prior Art
FIG. 1 shows a construction of a conventional color filter for a liquid crystal display. The color filter is composed of a transparent insulating substrate 1, a plurality of black matrices 2 formed on transparent substrate 1, color elements of red, green and blue, selectively formed between black matrices 2, a protective layer 4 formed on the color elements and black matrices 2, and a transparent conductive layer 5, formed on the protective layer 4.
FIGS. 2A to 2C are views explaining a method of producing a conventional color filter having the above construction. First, as shown in FIG. 2A, black matrix 2 is formed on substrate 1 by photolithography process using a photo-mask having a predetermined pattern after sputtering or evaporating metals such as chrome aluminum, etc. on substrate 1.
Black matrix 2, as is well known, has functions of increasing the color contrast of the LCD and preventing an increase of an off-current of a thin film transistor by external light, Which is used as a switching device for driving a liquid crystal display. Also, black matrix 2 can be formed by the same photolithography process as above after a photo sensitive black polymer is applied on substrate 1. Next, color elements 3 of red, green and blue are formed between black matrices 2 as shown in FIG. 2B. In forming color elements 3, the following methods are commonly used:
1) On a substrate on which black matrices 2 are formed, a photosensitive and dyeable polymer such as gelatin, casein, etc. is applied and then is exposed to light and developed to be patterned. This polymer-patterned substrate is dyed with a predetermined color in a dyeing reservoir and then is resist-processed with tannin acid, etc. By repeating the above process three times according to the red, green and blue colors, the forming of color elements 3 is completed.
2) As shown in FIGS. 2A to 2D, on a substrate 1 on which black matrices 2 are formed, a color resist of dispersed pigment is applied and then is exposed to light with a predesigned photo-mask to be patterned. By repeating the above process three times according to the red, green and blue colors, the forming of color elements 3 is completed.
3) Color elements 3 of red, green and blue are formed by printing in ink of desired colors by rollers on substrate 1 on which black matrices 2 are formed. After color elements are formed as above, as shown in FIG. 2C, protective layer 4 is evaporated thereon with a transparent material such as an acryl resin, an epoxy resin, a polyvinyl alcohol, a polyimide, a polyurethane, etc., and then transparent conductive layer 5 of indium tin oxide is evaporated by sputtering or vacuum evaporating, so that a color filter for a liquid crystal display is completed.
FIG. 3 shows a construction of another type of a conventional color filter for a liquid crystal, display. This color filter is composed of transparent insulating substrate 1, a transparent conductive layer 15 formed thereon, color elements 3 and black matrices 2 formed on transparent conductive layer 15 and a protective layer 4 formed on color elements 3 and black matrices 2.
The method of producing a conventional color filter having the same construction as above is as follows. As shown in FIG. 4A, transparent conductive layer 15 of indium tin oxide is evaporated on transparent insulating substrate 1 by sputtering or vacuum evaporating, and then a color resist is applied thereon and exposed to light through a predesigned photo mask and developed, so that red color elements 3 are formed, and then this is dipped into a developing liquid to develop the remaining color resist. By the same method as above, green and blue color elements 3 are also formed, and the resultant color filter from this process is shown in FIG. 4B. Next, black matrices 2 are formed by self-align or electric deposition of a photosensitive black polymer on color elements 3, and a protective layer is formed thereon to complete a color filter as shown in FIG. 4C.
However, according to the above-described conventional method of producing a color filter for a liquid crystal display, the evenness of the color filter layer is low due to the difference in height between black matrices and color elements. Further, since the black matrices are formed by the method of self-alignment or electric depositing, there is a defect in that the processing is complicated.